RIVERSIDE — A former student at UC Riverside was arrested Saturday in connection with a homemade firebomb and a pair of threatening letters found on campus that forced the cancellation of exams and a graduation ceremony, authorities said.

Audley Yung, 22, of Richmond was arrested about 2 p.m. on suspicion of possession of a destructive device, arson and making terroristic threats, campus police said in a statement. His bail was set at $25,000.

Final exams and the graduation ceremony for the school of business administration were scrapped Friday after groundskeepers found two plastic bottles that possibly contained flammable liquid near a burning palm tree outside the life sciences building early in the morning, authorities said.

Another suspicious device was found hidden in a planter near that building three hours later, and two threatening letters were received in the afternoon.

Yung attended UC Riverside in 2002 and 2003, and took summer session classes as recently as 2006, authorities said.

Five more graduation ceremonies, including one for about 600 students in the College of Humanities, Arts and Social Sciences, were held under tight security Saturday but went smoothly, school officials said.

An increased number of campus police officers barred guests from bringing in backpacks, and they searched purses and camera bags.

One graduate’s brother said he couldn’t get a clear shot of the stage with his video camera because so many security officials were in the way.